1. Field of the Invention
The present invention relates to a signal lamp for a vehicle such as a tail lamp, a stop lamp, a turn signal lamp, or the like. More particularly, the present invention relates to a signal lamp for a vehicle using a plurality of light-emitting diode (hereinafter referred to as LED) lamps as a light source.
2. Background Art
FIGS. 1 and 2 illustrate a conventional signal lamp 90 for a vehicle using a plurality of LED lamps 91 as a light source. By way of example, the plurality of LED lamps 91 are arranged in rows and columns to correspond to a light-emitting surface 90a of the signal lamp 90 for a vehicle. The plurality of LED lamps 91 are mounted on, e.g., a printed circuit board 92 and disposed in a housing 93. There is also provided an outer lens 94 for covering the LED lamps 91 in opposing relation to the light-emitting surface 90a.
The LED lamps 91 has a beam-like light distribution property with a comparatively narrow illuminating angle. To confer a desired light distribution property to the signal lamp 90 for a vehicle, lens cuts 94a corresponding to the individual LED lamps 91 are imparted to the outer lens 94. The lens cuts 94a allow light beams from the LED lamps 91 to be diffused properly.
Since the LED lamps 91 have narrow illuminating angles in the conventional signal lamp 90 for a vehicle thus constructed, light beams from the adjacent LED lamps 91 are not diffused sufficiently. Thus, when the light beams from the adjacent LED lamps 91 reach the outer lens 94, overlapping portions therebetween may be very little (see FIG. 2). In other words, the outer lens 94 has portions on which the light beams are not incident. This satisfies the specifications of the signal lamp 90 in terms of the light distribution property but bright portions with the incident light and dark portions without the incident light are observed when the light-emitting surface 90a of the outer lens 94 are viewed directly by a viewer, resulting in a speckled pattern (see FIG. 1). What results is the problem of a significantly impaired appearance of the lamp for a vehicle.
The above mentioned problem can be solved by reducing the pitch of the LED lamps 91 disposed. In this case, however, the pitch reduced to 1/2 quadruples the number of LED lamps 91 to be mounted in the housing 93. This leads to some new problems of a temperature rise or a higher cost due to an increased number of LED lamps 91 to be mounted as well as an increased number of mounting steps during manufacturing.